This invention relates to block and tackle equipment and more particularly to equipment known as a "swivel base" that is used on a large variety of sailing craft. The swivel base is normally affixed to the craft and is used to support an upstanding block or pulley. In addition, the base supports an outwardly extending arm having one end rotatably mounted on the base and the other end carrying a cleat or line securement device.
In using the aforesaid arrangement, a line is passed between the pulley and the base, and the bitter end is led to the securement device on the arm, typically a cam cleat. The other end of the line is normally attached to a sail, boom or other working parts such that the operator can make adjustments by either pulling in or releasing the line and then securing the bitter end to the line securement device.
As a specific example of the foregoing, swivel bases are beneficially employed in main sheet systems, the working end of the line attached to the boom and passing through a plural block sysem and downwardly around the block of the swivel base. The arm and block on the centrally mounted swivel base are capable of rotating about a common axis and are rotated from one side to the other when changing tacks, thus allowing the bitter end of the main sheet to be directly and freely accessible to the operator. The arm typically extends upwardly and outwardly from the base, allowing better or more convenient access to the securement device.
Although the basic form of a swivel base is known per se, all known constructions have the common problem of tending to fatique, loosen and become sloppy due to considerable repeated bending moments exerted on the lever arm. Excessive free play in the lever arm greatly increases the difficulty of releasing the line from the securement device. Also, bending moments on the block and arm are concentrated in the swivel base, causing uneven bearing load, which may result in binding in the pivot or failure of the base.
Prior art swivel bases have utilized small diameter sliding bearing surfaces for supporting the block and the arm, but such arrangements have not proved sufficiently durable to withstand the considerable loads and bending moments exerted thereon.